The invention relates to a system for coupling at least one DC source to a controllable energy store and to a method for operating the system according to the invention.
It is emerging that in future both stationary applications, such as wind power installations, and vehicles, such as hybrid or electric vehicles, will involve the increasing use of electronic systems that combine new energy storage technologies with electrical drive engineering. In conventional applications, an electric machine that is implemented, for instance, as a three-phase machine is operated by means of a converter in the form of an inverter. Characteristic of systems of this type is what is known as a DC intermediate circuit, via which an energy store, usually a battery, is connected to the DC side of the inverter. In order to be able to satisfy the power and energy requirements for a particular application, a plurality of battery cells are connected in series. Since the current provided by an energy store of this type must flow through all the battery cells, and since one battery cell can only conduct a limited current, additional battery cells are often connected in parallel in order to increase the maximum current.
Connecting a plurality of battery cells in series, besides creating a high total voltage, also entails the problem that the entire energy store fails if a single battery cell fails, since no battery current can then flow any longer. Such failure of the energy store can lead to failure of the entire system. In a vehicle, failure of the drive battery can result in the vehicle “breaking down”. In other applications, such as the adjustment of the rotor blades in wind power installations, dangerous situations can even result from unfavorable circumstances such as heavy wind. For that reason, high reliability of the energy store is always desirable, where “reliability” refers to the capacity of a system to work perfectly for a specified time.
The earlier applications DE 10 2010 027857 and DE 10 2010 027861 describe batteries with a plurality of battery module lines that can be connected directly to an electric machine. The battery module lines in this case have a plurality of battery modules connected in series, where each battery module has at least one battery cell and an associated controllable coupling unit that makes it possible, in response to control signals, to interrupt the particular battery module line, or to bypass the at least one battery cell respectively associated with it or to connect the respective associated at least one battery cell into the particular battery module line. Through appropriate actuation of the coupling units, e.g. with the aid of pulse width modulation, it is also possible to provide suitable phase signals for controlling the electric machine, so that a separate pulsed inverter can be omitted. The pulsed inverter required to control the electric machine is thus, so to speak, integrated in the battery. For the purposes of the disclosure, the full scope of these two earlier applications is incorporated into the present application.
If batteries of this type are employed in, for instance, electric vehicles, it should be noted that battery technologies available nowadays significantly limit the range of the electric vehicles.